Traditional database systems have been in existence for some time and are employed to serve the needs of many different information uses. Such database systems are typically referred to as persistent systems where data is stored and later accessed for processing, analysis, mining, etc. However, such traditional persistent systems do not support a new class of continuous time-varying data as in stream-based data systems. Stream-based data systems can be found in applications where data is continuously received asynchronously such as in web applications (website visits), financial institutions, sensor systems, and telecommunications environments (e.g., call records), for example. While users have become adept at programming for persistent data systems, the learning curve is more difficult for stream-based systems.